NAME

acos - arc cosine function

 SYNOPSIS

#include <math.h>

double acos(double x);

 DESCRIPTION

The acos() function computes the principal value of the arc cosine of x. The value of x should be in the range [-1,1].

An application wishing to check for error situations should set errno to 0 before calling acos(). If errno is non-zero on return, or the value NaN is returned, an error has occurred.

 RETURN VALUE

Upon successful completion, acos() returns the arc cosine of x, in the range [0, ] radians. If the value of x is not in the range [-1,1], and is not ±Inf or NaN, either 0.0 or NaN is returned and errno is set to [EDOM].

If x is NaN, NaN is returned and errno may be set to [EDOM]. If x is ±Inf, either 0.0 is returned and errno is set to [EDOM], or NaN is returned and errno may be set to [EDOM].

 ERRORS

The acos() function will fail if:

[EDOM]

The value x is not ±Inf or NaN and is not in the range [-1,1].

The acos() function may fail if:

[EDOM]

The value x is ±Inf or NaN.

No other errors will occur.

 EXAMPLES

None.

 APPLICATION USAGE

None.

 FUTURE DIRECTIONS

None.

 SEE ALSO

cos(), isnan(), <math.h>.

DERIVATION

Derived from Issue 1 of the SVID.